Issues with Fuse#12 on my 1991 244

Yesterday, after checking the readings at the ECU (see other thread), I turned car on and backed it into an alley. Car was behaving normally.

Let her idle for a couple of mins and came back to find fuse#12 was blown. None of the accessories were on except the volt gauge which is powered off fuse 12 and the reverse switch when I backed the car out.
Took her for a short drive to measure ECT values.

Came back, put in a new 8A fuse and started the car again. New fuse did not blow, however, everything on that circuit does not work.

Additionally, this might be a separate issue, but my instrument panel lamps/center console lamps all stopped working last week The respective fuse is fine and the exterior lights all come on as they should.

Once again, can someone point me in the right direction?

For the instrument cluster lighting and center section lights. Start with the dimmer. Check it and make sure it's not turned so the lights are off. Then use a test light to check that it gets 12v in and puts out voltage to the lights which will vary with where it's turned.

For the fuse 12 stuff. A manual car has wiring under the car for the reverse lights. Very often the wiring decays and can cause a blown fuse. The wiring also can wear through on the edge of the body on the shifter hole where it passes through. An auto does the reverse lights on the nertral safety swtich so that wiring should be checked to make sure it isn't damaged around the shifter.

If everything doesn't work on a circuit. I would test the fuse by using the test light and use a test light to verify the circuit is getting power out to the various loads on the circuit.

For fuse #12, I looked briefly at the wiring diagrams and my top guess would be that the seat belt reminder light in the back of the center console has come loose and is shorting to ground.

That makes sense as I had pulled the center console out to use the little ground screw (the one with a million wires going to it right behind the AC switch on the passenger side) as my ground point while measuring values at the ECU.

I will investigate this hopefully tomorrow. Interestingly, even the rear defroster which I don't believe is wired to fuse 12 is not working. Fuse 12 does not blow anymore though....

dl242gt - good point on the dimmer. I have it turned to the brightest spot. Couple of years ago I had the same issue due to resistance building up due to a leaky windshield gasket. That was fixed later thought by going to the new style windshield gasket. Any way to check using a DMM?

Neutral safety switch on the car has been jacked up ever since I bought the car up. Doubtful if that's what caused but worthwhile investigating.

With the dimmer you can test it with a voltmeter or a test light. You should have 12V and a very bright test light on the input. The output should vary as you turn it and the bulb or voltage output will show the change. Look for open spots as you turn it where the test light goes out or voltage disappears.

They also get high resistance as they get old and just have a low output even when turned so the lighting should be a max. You will see low voltage or a dim test light if that is happening.

bobxyz said:

For fuse #12, I looked briefly at the wiring diagrams and my top guess would be that the seat belt reminder light in the back of the center console has come loose and is shorting to ground.

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Whatever fuse is for the power windows, this has happened to me many times when my center console broke and one of those wires made contact with a ground. So I wrapped it up with electrical tape and no problems since.

Dl242gt - you were spot on. The rheostat was shot. It was barely allowing any voltage at all throug it. Swapped it and I have my dash lights back.

As for the primary problem, I can’t find any broken wires at all behind the center console. Is there a specific location to search?
Currently, I don’t have power windows, rear defrost, air conditioning,
Blower works as do hazard, radio and cigarette lighter/12V outlet.

Edit: I verified that I get 12V on the right side of fuse 12 (this one includes AC, heated rear window, seat belt reminder and window lifts as well) and 12V at the right side of fuse 10 (power window lift).

So what the heck is going on here?

Edit 2: verified 12V at pin 1 of the turn signal relay (it’s the one just below and to the right of the AC fan speed knob). Pin 1 is 2 wires blue/yellow each. Pin 2 which is two wires, both of which are white/red to be at 0.22V. Moving the indicator stalk to up or down did nothing.
Found another relay tucked farther down at the bottom right of the center console. Relay is M.Diod/040990. Key in KPII - The pink wire on this gave 12V and the blue/yellow gave 12V as well. However, the wire harness on this one is going below the carpet and towards the shifter.

F@&$!!!!! There’s a definite short somewhere that I can’t trace for sure.

Started her back up and holy crap. She’s running really bad - shaking and stumbling around like she wants to die. It’s definitely running rich, smells like gas

This car is possessed.

Damn that is an unruly beast. Since you know the suspected circuit is fuse 12. You can take the load side(right side) connections off one at a time to see which circuit is the problem one. The window wiring can get damaged inside the door and inside the accordian thing that brings the wires from the car to the door. If the insulation does the flake away thing wires can short to each other. I had this happen on central locking for example.

With power off. You can use an ohm meter on each load wire to see which one gives a short. Or you can just disconnect them one at a time and see which one stops the fuse from blowing.

Floor console wiring is common. Unplug it all and try again.

When I said "center console" I meant the one between the seats that houses the parking brake lever, and the seat belt reminder light for the back seat passengers. Sorry for the confusion.

Fuse 12

If the wiring is as built, and on TB that's a big if:

Fuse 12 has nothing to do with instrument lighting dimmer or backup (reverse) lighting circuits.

For the power windows, it only powers the relay coil (the one that keeps you from using the windows without the key) so no use delving into the door jam wiring.

Fuse 12 is the one that always brings to mind a Swedish engineer's unconscious aggression toward US air conditioning addicts, because when the AC clutch wire's insulation gets rubbed off vibrating on the compressor, the resulting blown fuse keeps one from getting heat relief by rolling down the windows.

Yes, it could be the blue/yellow on its way to the rear seat belt reminder light, but that one was pretty well protected compared with the ash tray lighting that's on fuse 16.

And it could be the cruise circuit too, but again, unless these better protected circuits have been tinkered with, it isn't likely. Suspect where it connects to the switch in the stalk on the steering column.

Rear window defrost was put on fuse 11.

And yes, there's a typo in the green manual detail pages showing fuse 12 runs the backup lights. It is correctly identified as fuse 5 in the fold-out (main) wiring diagram.

Isolating the load at the fuse panel can be difficult because not all the loads have their own wire, or the female spade terminals has two wires crimped.

To check the issue I think is most common (the AC) just turn off the snowflake switch.

If the car's an automatic, and you've been inside the shifter, check the blue/yellow to the parking shift lock relay.

Lots of good insight here. I checked the wiring to the rear seat belt warning wiring and it looks fine. That being said, both the lights have never come on the entire 6 years I have owned the car. Perhaps I should investigate this further...

Behind the center console, there's a relay to the left (toward's the drivers side) of the 2 central door lock relays. Tapping on that seems to have fixed the problem. Jiggling and moving the wires to this relay seemed to help as well somewhat. I think it's the relay that's starting to flake out. Anyone know what that relay is?

240-FAN said:

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Behind the center console, there's a relay to the left (toward's the drivers side) of the 2 central door lock relays. Tapping on that seems to have fixed the problem. Jiggling and moving the wires to this relay seemed to help as well somewhat. I think it's the relay that's starting to flake out. Anyone know what that relay is?

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Guessing you're referring to the headlight relay. The only sure way to identify relays is by noting the color codes of the wires connected to them. The headlight relay is usually OK, but its socket burns up when the connections get oxidized.



The headlight relay is the one on the rail to the left of the central locking relays with the white socket having thick yellow and green/red wires. Check the socket around the green/red and yellow wires for meltage. Save the relay, it is probably still good and is not a common cube relay.

Yep, that white colored relay. Thank you Art!